Horstmann H37XL Channelplus Electronic Central Heating Programmer Series 2 - 3 channel, 7 day

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Finally on the programmer what would be the point in providing term 3 to be live when the heating was off. ChannelPlus H37XL Series 2 Controlling 3 x two port spring return zone valves via RoomStat and CylinderStat giving independent control of Hot water and two zones of Heating. Ideal for the control of two heating zones as well as hot water via separate thermostats and zone valves (e.g. zones 1, 2 and 3 or hot water, heating 1 and 2).

Insert a wire link between the terminals where the two switching wires have just been removed from, so that they are now electrically joined together. INSTALLATION AND CONNECTION SHOULD ONLY BE CARRIED OUT BY A SUITABLY QUALIFIED PERSON AND IN ACCORDANCE WITH THE CURRENT EDITION OF THE IEE WIRING REGULATIONS. The reason I say this is because I connected the blue wire to this as your original instruction and the Nest never worked. I wondered if this only went live when the desired temperature was reached and it received a signal from the thermostat?

I have only ever once come across a system with a 'central heating off' connection that contained a very uncommon type of motorised valve (MoMo, or Motor on, Motor off) that requires this connection to close it.

For reasons of space and clarity the diagrams has been simplified, for instance some Earth connections have been omitted. Other control components shown in the diagrams i.e. Valves, RoomStats etc. are general representations only. However the wiring detail can be applied to the corresponding models of most manufacturers e.g. Horstmann, Honeywell, Danfoss Randall etc. Designed for use with fully pumped central heating systems, using three separate two-port zone valves. This will also be the case with the "similar Horstmann programmer" in your last post. The reason common terminals are provided outside of the unit, rather than connected to 230v inside, is so that they can be used to switch other voltages (some boilers use 24v) if required]In reality, the blue wire may not be actually doing anything, but only the original installer would know. However as I said earlier, you are simply exchanging one electrical switch for another and the corresponding terminal at the Heatlink would be (1) Heating Satisfied.